This application is based on Japanese Patent Application No. 2002-311260 filed on Oct. 25, 2002, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention is related to an ejector (refer to JIS Z 8126 number 2. 1. 2. 3) for transmitting a fluid by entrainment function of a driving fluid jetted at a high speed, and an ejector cycle using the ejector. The ejector has a throttle variable nozzle.
2. Related Art
In an ejector cycle, low-pressure side refrigerant (i.e., refrigerant in an evaporator) circulates by pumping operation of an ejector as generally known. Besides, a suction pressure of refrigerant to be sucked to a compressor is increased while converting expansion energy into pressure energy in the ejector so that power consumption of the compressor is decreased. However, when energy conversion efficiency in the ejector (i.e., ejector efficiency) is decreased, the suction pressure of the compressor cannot be sufficiently increased in the ejector, and power consumption of the compressor cannot be sufficiently decreased. Besides, a sufficient amount of the refrigerant cannot be circulated into the evaporator.
On the other hand, when a nozzle inside the ejector is a kind of a fixed throttle, an amount of the refrigerant flowing into the nozzle has a fluctuation, and nozzle efficiency and ejector efficiency vary in accordance with the fluctuation. Here, the nozzle efficiency is a conversion efficiency when pressure energy is converted to speed energy in the nozzle. Ideally, a throttle opening degree of the nozzle is preferred to be variably controlled in accordance with a flow amount of refrigerant. However, according to experiments by the inventors of the present invention, when the throttle opening degree of the nozzle is simply changed, the nozzle efficiency may be considerably deteriorated.
It is an object of the present invention to provide an ejector capable of controlling its nozzle throttle opening degree while improving the nozzle efficiency.
According to a first aspect of the present invention, an ejector includes a nozzle having an inner wall surface for defining a fluid passage through which a drive fluid flows, a pressurizing section in which a fluid is sucked by entrainment of a jet flow of the drive fluid jetted from the nozzle and is mixed with the drive fluid jetted from the nozzle, and a needle valve for changing a throttle opening degree of the fluid passage in the nozzle. Further, the nozzle includes a throat section having a cross-sectional area (i.e., inner diameter) that is the smallest in the fluid passage, and the needle valve is disposed to be displaced in an axial direction in the fluid passage of the nozzle. In addition, the needle valve has an end section formed in a tapered shape so that a cross-sectional area of the needle valve decreases toward a top end of the needle valve, the end section of the needle valve reaches to a downstream side of the throat section in a flow direction of the drive fluid at least when the throttle opening degree is minimum, and the fluid passage of the nozzle has a substantially constant cross-sectional area in a downstream section downstream from the throat section.
Accordingly, a cross-sectional area of a substantial refrigerant passage defined by an inner wall surface of the nozzle and the needle valve in the downstream section is gradually increased in accordance with the tapered shape of the needle valve. Therefore, it can prevent a pressure loss due to a rapid expansion of the passage area in the nozzle. Thus, it is possible to control the throttle opening degree of the nozzle while the nozzle efficiency can be improved. Further, the fluid passage of the nozzle has a substantially constant cross-sectional area, in a downstream section downstream from the throat section. Therefore, it is no need to form a diffuser section having a gradually increasing inner diameter. Thus, the nozzle having the throat section can be readily formed.
According to a second aspect of the present invention, the fluid passage is formed into a tapered shape having a cross-sectional area that is gradually decreased by a taper angle xcex81 toward an outlet of the fluid from a downstream side of the throttle section to at least the throat section, and the taper angle xcex81 of the fluid passage is smaller than a taper angle xcex82 of the tapered end section of the needle valve. Therefore, the cross-sectional area of the substantial refrigerant passage defined by the inner wall surface of the nozzle and the needle valve in the downstream section can be gradually increased in accordance with the tapered shape of the needle valve. In the present invention, the fluid passage can be formed into a multi-step tapered shape tapered in multiple steps.
Preferably, the throat section has an inner periphery surface formed in a curved shape. In this case, the passage sectional area of the fluid passage can be continuously smoothly changed. More preferably, the top end of the needle valve reaches to the downstream side of the fluid flow with respect to the throat section even when the throttle opening degree is maximum. Further, the end section of the needle valve can be formed into a conical tapered shape, or can be formed in a hanging bell shape.
Further, the ejector of the present invention can be effectively used for an ejector cycle. In this case, the nozzle of the ejector decompresses refrigerant flowing from a high-pressure heat exchanger, and the refrigerant in an evaporator (low-pressure heat exchanger) is sucked into the pressurizing portion by entrainment of a jet flow of the refrigerant jetted from the nozzle and is mixed with the refrigerant jetted from the nozzle in the pressurizing portion. In this case, the opening degree of the nozzle can be controlled without reducing the nozzle efficiency and ejector efficiency. Therefore, the ejector cycle can be effectively operated.